Automatic positioning and adaptation in an adjustment for a shim field map

Abstract

A method for shimming a magnetic field in a magnetic resonance tomography (MRT) device includes determining a field of view region for an object under examination. Determining the field of view region includes adapting the field of view region automatically to a region of the object under examination to be examined by the MRT device. Before the MRT device records an image, an adjustment measurement of the magnetic field is performed. A field map of the magnetic field of the field of view region is defined based on the adjustment measurement. A shimming of the magnetic field is implemented based on the field map.

The invention claimed is: 
     
       1. A method of shimming a magnetic field in a magnetic resonance tomography (MRT) device having a local coil, the method comprising:
 determining, by a controller of the MRT device, a field of view area; 
 automatically adapting the field of view area to an area of an object under examination; 
 determining, by the controller, a shim field map of the field of view area by using automatic positioning information and automatic coverage information including the area of the object under examination and a position of the local coil, wherein the MRT device is configured to use the area of the object under examination and the position of the local coil in order to determine a position, a size, or the position and the size of the field of view area; 
 shimming the magnetic field of the field of view area with respect to the object under examination based on the determined shim field map; 
 recording, by the MRT device, an image of the object under examination using the shimmed magnetic field; and 
 displaying or storing the recorded image. 
 
     
     
       2. The method as claimed in  claim 1 , wherein the determining of the field of view area with the controller comprises automatically defining the field of view area whereby the field of view area is adapted in the position, the size, or the position and the size to the area of the object under examination. 
     
     
       3. The method as claimed in  claim 2 , wherein the field of view area is smaller than a maximum possible field of view area of the MRT device. 
     
     
       4. The method as claimed in  claim 2 , wherein the field of view area is defined whereby at least an entire area to be examined by the MRT device is contained in the field of view area. 
     
     
       5. The method as claimed in  claim 2 , wherein the field of view area is defined whereby an edge length of the area of the object under examination fills out at least a predetermined proportion of an edge length of a maximum possible MRT field of view of the MRT device. 
     
     
       6. The method as claimed in  claim 2 , wherein the field of view area is defined whereby an edge length in a first direction of the area of the object under examination fills out at least 10 percent of an edge length of a maximum possible MRT field of view of the MRT device, and an edge length in a direction of the area of the object under examination perpendicular to the first direction fills out at least 10 percent of an edge length of the maximum possible MRT field of view of the MRT device. 
     
     
       7. The method as claimed in  claim 2 , wherein the shimming of the magnetic field comprises shimming only in the field of view area. 
     
     
       8. The method as claimed in  claim 2 , wherein a calibration measurement of the magnetic field in the field of view area in determining the shim field map is:
 (1) an accelerated calibration measurement that is compared to a calibration measurement of the magnetic field in a maximum possible field of view area, 
 (2) a calibration measurement with a greater resolution that is compared to the calibration measurement in the maximum possible field of view area, or 
 (3) a combination of (1) and (2). 
 
     
     
       9. A magnetic resonance tomography (MRT) device comprising:
 a local coil; 
 a controller configured to:
 define a field of view area taking into account an area of an object under examination to be examined by imaging by the MRT device, wherein the area to be examined is contained in the field of view area; and 
 determine a shim field map of the field of view area by using automatic positioning information and automatic coverage information including the area of the object under examination and a position of the local coil, wherein the MRT device is configured to use the area of the object under examination and the position of the local coil in order to determine a position, a size, or the position and the size of the field of view; and 
 
 a shim device configured to shim the magnetic field in the MRT device based on the determined shim field map, 
 wherein the controller is configured to control the shim device based on the determined shim field map, and 
 wherein the MRT device is configured to record an image of the object under examination using the shimmed magnetic field, and display or store the recorded image. 
 
     
     
       10. The MRT device as claimed in  claim 9 , wherein the controller is configured to define the field of view area whereby the field of view area is adapted automatically to the area of the object under examination. 
     
     
       11. The MRT device as claimed in  claim 10 , wherein the controller is configured to define the field of view area whereby the field of view area is automatically adjusted in the position, the size, or the position and the size to the area of the object under examination. 
     
     
       12. The MRT device as claimed in  claim 11 , wherein the controller is configured to define the field of view area whereby the field of view area is smaller than a maximum field of view area of the MRT device. 
     
     
       13. The MRT device as claimed in  claim 11 , wherein the controller is configured whereby at least an entire area of the object under examination is in the field of view area. 
     
     
       14. The MRT device as claimed in  claim 9 , wherein the shim device is configured to perform a shimming only in the field of view area. 
     
     
       15. The MRT device as claimed in  claim 9 , wherein the controller is configured to determine the shim field map with a calibration measurement of the magnetic field in the field of view area, and
 wherein the calibration measurement is: 
 (1) an accelerated calibration measurement that is compared to a calibration measurement of the magnetic field in a maximum possible field of view area, 
 (2) a calibration measurement with a greater resolution that is compared to the calibration measurement in the maximum possible field of view area, or 
 (3) a combination of (1) and (2).